1. Field of the Invention
The present invention relates to a fine particulate crosslinked type N-vinylcarboxylic acid amide resin, a microgel of the crosslinked type N-vinylcarboxylic acid amide resin comprising said resin swelled (gelled) with water or an organic solvent, and a thickener, dispersion stabilizer or lubricant comprising said microgel as the main component. More specifically, the present invention relates to a fine particulate crosslinked type N-vinylcarboxylic acid amide resin having an excellent chemical stability and affinity for water and organic solvents such as alcohols, particularly exhibiting a high thickening ability, dispersion stability and lubricity by absorbing a liquid in which inorganic or organic ions coexist in the system to be gelled, a microgel having a wide usage in various fields due to the excellent characteristics and functions of said resin, and a hydrophilic (organic solvent-philic) thickener, dispersion stabilizer or lubricant comprising said microgel as the main component.
2. Description of the Related Art
In the prior art, fine particles of a crosslinked hydrophilic gel exist as a dispersion of swelled fine particles in water, and the dispersion thereof is a non-Newtonian flow even at a low concentration, and exhibiting a remarkably high viscosity different from that of a water-soluble linear polymer which exists as a solution in water, as is widely known in the art, and has been variously utilized as a thickener, dispersion stabilizer, lubricant for aqueous gel-like products and cosmetics.
As the crosslinked type fine particles known in the art, for example, synthetic polymers such as the crosslinked type polyacrylic acid (carboxyvinyl polymer) and the crosslinked type acrylic acid copolymer may be included.
These crosslinked type fine particles, however, are all crosslinked products of the polymeric electrolyte type, and therefor, exhibit an excellent thickening ability for water containing no electrolyte but exhibit only remarkably low thickening ability for an aqueous liquid containing a large amount of organic or inorganic ions, such as a natural extract, surfactant, perfume, colorant, reactive dye for printing, and cement slurry. This is considered to be a result of a reduced expansion of the chains because of a suppression of a dissociation of the polymeric electrolyte, which is the backbone chain of the crosslinked product in the presence of ions. Further, when polyvalent metal ions exist, an ion crosslinking occurs through the backbone carboxylic acid, whereby a crosslinked polymer with a substantially higher crosslinking density than required is formed, and this lowers the thickening ability.
To overcome the drawback mentioned above, Japanese Unexamined Patent Publication (Kokai) No. 59-232107 discloses crosslinked type fine particles comprising acrylic acid or methacrylic acid ester copolymerized therein as the crosslinked type acrylic acid copolymer fine particles. This method obtains ion resistant crosslinked type fine particles by introducing nonionic and lipophilic backbone chain constituting units into the polymeric electrolyte backbone chain, but the ratio of (meth)acrylic acid ester copolymerized is as small as 3.5% by weight or less, and the ion resistance is not always satisfactory. Further, if the amount of the hydrophilic monomer is increased, the affinity for water may be lowered, and thus a possibility exists that a transparent gel-like product can not be obtained.
In water absorptive resins known in the art, an aqueous dispersion thereof exhibits a viscosity, but because of greater particle size, the system as a whole becomes nonuniform and therefore, does not exhibit a thixotropic viscous behavior.
Further, among natural polymers, such as those which are not fine particles but exhibit a viscous behavior similar to the crosslinked type fine particles, there may be included natural gums such as gum tragacanth, locust bingham, sodium alginate, carrageenan, and guar gum. These natural polymers, although they contain the groups of electrolytes, exhibit a relatively good thickening ability also for an aqueous liquid containing a large amount of ions. Natural polymers, however, are not only cost-inefficient, but also are susceptible to attack by microorganisms, bringing the problem of corruption, and have a peculiar color and odor, and thus the scope of use thereof is limited.
Crosslinked type fine particles can be obtained according to the preparation processes, in addition to Japanese Unexamined Patent Publication (Kokai) No. 59-232107 described above, disclosed in Japanese Unexamined Patent Publication (Kokai) Nos. 59-80411 and 2-258813, by carrying out a precipitation polymerization in an organic solvent. The crosslinked type fine particles also can be prepared by polymerizing an acrylic acid monomer in an aqueous concentrated solution of a salt. In these publications, however, a preparation example using an N-vinylamide compound is not disclosed.